# 5 bit 2's complement or 1's complement adder

Discussion in 'Homework Help' started by Hazard111, Jan 4, 2015.

1. ### Hazard111 Thread Starter New Member

Jan 1, 2015
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I know how to make 5 bit 2's complement adder and 5 bit 1's complement adder separately can someone give mi idea how to make adder that depending on signal can add works as 5 bit 2's complement or 5 bit 1's complement adder

2. ### WBahn Moderator

Mar 31, 2012
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5,755
This is getting a bit old. You post a question, don't show your work and when asked to show your work you simply start a new thread with essentially the same question, apparently hoping to bait someone into doing your work for you. Doesn't work like that.

SHOW YOUR WORK!

You say that you know how to do a 2's comp and a 1's comp adder separately. Okay. Fine. Let's see them.

Then describe what you see as the key differences and similarities they share that you might exploit to convert one into the other based on a control signal input.

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3. ### WBahn Moderator

Mar 31, 2012
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So what are the differences and similarities between the two?

Are you trying to implement an adder, or an adder/subtractor? Do you need overflow detection?

Do you understand how both of those circuits that you copied from somewhere actually implement addition and subtraction?

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4. ### WBahn Moderator

Mar 31, 2012
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A two's complement adder doesn't do anything to the input. Now, a two's complement subtractor does. That's why I asked if you need to make an adder or an adder/subtractor.

The 1' complement circuit you posted doesn't do overflow detection, yet you said that you need overflow detection.

In general, if I have two signals and sometimes -- determined by a control signal -- I want to see one of them and other times I want to see the other, what is a straightforward way to accomplish that?

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5. ### WBahn Moderator

Mar 31, 2012
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I'm not even going to try to follow this. Please show a schematic of what you are proposing.

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